This invention relates to a shear for shearing a material during its movement and, more particularly, to a pendulum-type flying shear for shearing a material moving between vertically movable cutting blades within a frame mounted on a crank shaft, while the frame is subjected to an oscillating movement.
In such a pendulum-type flying shear, the energy required for shearing the material is equal to the speed of the material passing through the shear multiplied by the cross-section of the material, as is same as in the theorem of continuity in the field of the fluid dynamics. In a specific shear, therefore, it will be necessary to reduce the shearing speed or the speed of movement of the material to be sheared, when the latter has a larger cross-section.
It will, therefore, be understood that if a steplessly variable speed gear effective to the pendulum-type flying shear is provided therein materials having large and small cross-sections will be sheared by the single shear. However, there has never been such a steplessly variable speed gear as is of a large capacity, high efficiency and small and cheap type, and thus a direct current electric motor capable of making the speed control has hitherto been used to vary the shearing speed by controlling the speed of the motor itself. Furthermore, the speed varying operation can be achieved by combining a constant speed electric motor and a toothed wheel gearing, but such arrangement can not provide a steplessly variable speed transmission and the size of the speed gear and the required area of the installation are very large so that this system can not have been used.
In the pendulum-type flying shear operated by the speed control system with the direct current electric motor, the capacity of the motor is determined in consideration of the following conditions:
(i) Shearing energy or inertia energy should be generated which is required for shearing an allowable maximum cross-section of the material at an allowable minimum speed (condition to the maximum output), and PA1 (ii) said energy can be generated within the minimum shearing cycle (the shearing length divided by the maximum material speed) (the momentary output being large). PA1 (1) Published Japanese Patent No. 41-16477 PA1 (2) Published Japanese Patent No. 48-11554 PA1 (3) Published Japanese Patent No. 44-18039 PA1 (4) Iron and Steelworks Engineering (Journal of the Iron and Steel Institute, November, 1955, pages 239-240) PA1 (5) DEMAG W84.3 Pendulum Shear
In these two conditions, the second condition (ii) is closely concerned with the production efficiency, so that the minimum shearing cycle tends to become small, but, in this case, the capacity of the motor should become large and thus a large capacity of the motor is to be used. In case of using such a large capacity of the motor, however, there will be caused a problem that the efficiency is lowered when a large cross-section of the material is sheared at a low speed. This results from the fact that the efficiency of the motor is maximum when it is driven at the rated speed and lowers as it is driven at a low speed.
In addition, as the motor capacity becomes large, the control device and the power source installation will become large, and the installing cost and running cost will also become very high.
In the hot rolling installations, furthermore, for the purpose of recent improvement of the productivity and product quality, high speed and continuous rolling lines have been developed. As a result, it is required for the pendulum-type flying shear to provide a wide speed range from a high speed to a low speed and the shearing operation of a large cross-section of the material by a small power. However, as the speed of movement of the material becomes high and as the cross-section becomes large, the impact force applied to the shear when shearing operation becomes large, so that it becomes necessary to synchronize the shearing speed or the speed of movement along the line of the upper and lower cutting blades with the speed of movement of the material. The speed synchronization is an important factor in view points of not only lowering the impact force, but also shearing the material at the desired shearing position to enhance the shearing accuracy and provide a good sheared section.
Hitherto, as a flying shear for shearing a strip conveyed from a hot rolling mill, while the strip is moving, a drum type flying shear or a four-link type flying shear has mainly been used. The drum type flying shear is arranged such that upper and lower cutting blades are secured to a pair of rotating drums disposed on the upper and lower sides, respectively, of the material, the drums being rotated at a speed synchronized with the material speed to shear the material bitten between the blades. In this type of shear, however, there are problems that the blades are engaged with the material with an angle of inclination relative to the latter so that relative sliding movement is caused between the blades and the material, and the blades are interfered with each other and the adjustment of the gap between the blades or the lapping amount is difficult.
On the other hand, the four-link type flying shear is arranged such that two pairs of links for forming parallelograms on upper and lower sides and opposite sides, and upper and lower blades are secured to arms constituting the parallelograms and rotated in synchronous relationship with the speed of moving material to make the shearing operation. This type of shear is disadvantageous in that although the blades are vertically moved to provide a longer blade life than in the drum type flying shear there is required a relatively large number of arms forming the links and the installation becomes large and heavy in order to maintain a sufficient strength.
As a billet shearing device in a continuous casting installation, there has been known a so-called pendulum-type shear in which vertically movable cutting blades are provided within a frame oscillatingly mounted on a crank shaft to shear the billet between the blades, as described, for example, in Journal of the Iron and Steel Institute, November, 1955, page 6. In this type of shear, when the material is moved at a very low speed, such as within the range of 0.1 m/min to 2.0 m/min, as a billet, there is no problem, because the shearing operation is made with the frame urged as a pendulum by the material bitten between the blades, but such shear is unsuitable as a shear incorporated in a rolling line of the hot rolling installation in which the speed of movement of the material is very high, such as 10 m/min to 200 m/min, and the range of the speed to be selectable is large. Thus, the conventional pendulum-type shear is disadvantageous in that no means are provided for synchronizing the speed of the frame with that of the material and the impact between the blades and the material is too large to break the blades or/and shear in case of the hot rolling installation in which the speed of the material is large.
For the purpose of shearing a thin sheet, there has often been used a so-called oscillatortype flying shear in which the material is sheared by an upper cutting blade secured to an oscillating frame and a mating lower cutting blade movable upward and downward within the frame by an eccentric mechanism. However, this type of shear is also disadvantageous in that the center of gravity of the frame is positioned above the center of oscillation, so that the gravity due to the weight of the oscillating portion, in addition to the varying power, is applied thereto, and if the capacity of the shear increases the weight of the oscillating portion will accordingly become increased to provide a construction resisting the reaction force. Therefore, it is unsuitable for shearing a thick sheet.
The following are prior publications showing the background of the present invention.